This invention relates to a ballistics fire control solution process and apparatus for a spin or fin stabilised projectile particularly, but not exclusively, suitable for use with guns.
The trajectory of spin stabilised projectiles, such as rounds fired from conventional rifled gun barrels, or of fin stabilised projectiles, such as missiles fired from launchers, through the atmosphere conventionally is predictable by a process involving determining the trajectory of the projectile in three dimensional space as a function of time in flight, deriving the acceleration components acting on the projectile and using this data in fundamental equations of motion to derive the predicted trajectory. During Range and Accuracy firings of a projectile such as a gun round on a calibrated range, the ballistics and aerodynamic input parameters are tuned such that the trajectory predicted accurately matches independent, for example radar, measurements of the trajectory. This results in a so called calibrated trajectory for a particular round/fuse combination. This is a relatively time consuming process and cannot be carried out fast enough to enable a gun Fire Control Solution (FCS) to be achieved at a fast enough rate for use by a real-time FCS computer such as a GSA8. Hence the calibrated trajectory has been used to produce Designer Extended Range Tables from which the projectile launcher (such as a gun) azimuth and elevation orders could be determined for a given situation. A process of Range Table Reduction then has to be invoked where various two dimensional cubic-spline curve fitting to the Designer Range Tables has to be performed. The coefficients generated from the Range Table Reduction (curve-fitting) process then require to be implemented in a real time fire control solution computer.
A disadvantage of such conventional Range Table Reduction processes is that further approximations are introduced into the FCS and thus the computed gun orders in the real time FCS diverge from the values that would have been derived using the more accurate calibrated trajectories.
There is thus a need for a process and apparatus which can utilise calibrated trajectories for projectiles in a real time projectile Fire Control process.
According to one aspect of the present invention there is provided a ballistics fire control process for a spin or fin stabilised projectile, in which the closest point of approach between a fired projectile and a target is taken to be at the instant when the projectile velocity vector is orthogonal to the position error vector between the projectile and target, in accordance with the relationship:
Vpxe2x80xa2(Ppxe2x88x92PF)=0
where Vp is the projectile velocity vector, Pp is the projectile trajectory or position vector, PF is the target future position vector, xe2x80xa2 is the vector dot product and (Ppxe2x88x92PF) is the position error vector.
According to another aspect of the present invention there is provided a ballistics fire control process for a spin or fin stabilised projectile, including the steps of:
(a) tracking a target,
(b) producing a target position vector and a target velocity vector for the tracked target,
(c) producing a calibrated trajectory vector, a calibrated velocity vector and a time in flight value for the projectile, at current projectile launcher azimuth and elevation values,
(d) calculating the target future position vector from the target position vector, target velocity vector and projectile time in flight value,
(e) firing the projectile,
(f) calculating the achieved closest point of approach of the projectile to the target from the projectile calibrated trajectory vector, projectile calibrated velocity vector and target future position vector,
(g) comparing the achieved closest point of approach of the projectile to a desired zero value to produce an error value,
(h) integrating the achieved closest point of approach error value,
(j) calculating corrected projectile launcher azimuth and elevation values from the integrated achieved closest point of approach error value to drive the achieved closest point of approach towards zero and
(k) repeating steps (a) to (j) if necessary to produce a substantially zero achieved closest point of approach value of the projectile and target.
Preferably at the closest achieved point of approach the projectile velocity vector is orthogonal to the position error vector between the projectile and target in accordance with the relationship:
VPxe2x80xa2(Ppxe2x88x92PF)=0
where Vp is the projectile velocity vector, PP is the projectile trajectory or position vector, PF is the target future position vector, xe2x80xa2 is the vector dot product and (PPxe2x88x92PF) is the position error vector.
Conveniently the target future position vector is generated over the same simulated time-frame in which the projectile trajectory vector is generated and the target future position vector and projectile calibrated trajectory vector are differenced as a function of time to provide the achieved closest point of approach between the fired projectile and target.
Advantageously, the achieved closest point of approach is driven towards zero in steady state conditions.
According to a further aspect of the present invention there is provided a ballistics fire control systems for a spin or fin stabilised projectile including,
a target tracker for generating a target position vector and a target velocity vector,
means for generating a calibrated trajectory vector, a calibrated velocity vector and a time in flight value for the projectile at current projectile launcher azimuth and elevation values,
a target future position predictor for receiving from the generating means the projectile time in flight value and from the target tracker the target position vector and the target velocity vector and for calculating the target future position vector from the target position vector, target velocity vector and projectile time in flight,
a closest position of approach computer for receiving the target future position vector from the target future position predictor and the projectile calibrated trajectory vector and projectile calibrated velocity vector from the generator means and for calculating therefrom the achieved closest point of approach of the projectile to the target,
a comparator for receiving from the closest position of approach computer the achieved closest point of approach of the projectile and for comparing it to a desired zero value to produce an error value,
an integrator for receiving and integrating the error value from the comparator, and
a compensator for calculating corrected projectile launcher azimuth and elevation values from the integrated achieved closest point of approach error value to drive the achieved closest point of approach error value towards zero.
Preferably the target tracker is a radar unit or is an electro-optical unit.
Conveniently the compensator is operatively connectable to a servo mechanism forming part of a laying mechanism for the projectile launcher.
According to yet another aspect of the present invention there is provided a ballistics fire control systems according to the present invention in combination with a projectile launcher in the form of a gun.